The applicants' earlier patent application WO-01/75778 discloses several embodiments of localised yarn structures in woven, knitted and non-woven textiles that incorporate both electrically conductive and electrically insulative yarns for the purposes of constructing switches and pressure sensors therefrom.
These structures and arrangements of yarns are principally concerned with controlling the amount of electrical contact that occurs between two or more electrically conductive yarns, or analogous elongate electrical conductors, that cross over one another within the plane of the textile. Techniques are described in WO-01/75778 whereby the aforementioned electrically conductive yarns can be affixed in permanent electrical contact with one another, or permanently separated by insulative yarns and/or an air gap such that no electrical contact takes place between them.
Certain structures and manufacturing parameters allow for the latter (separated) case to become extended in function, such that the conductive yarns remain electrically separate until a mechanical force is exerted upon the textile structure in a direction substantially perpendicular to the plane of the fabric. Under this condition, one or other of the separated electrically conductive yarns can be made to traverse the separating air gap and/or push aside the insulative elements and thus be brought into electrical contact with the other conductive yarn or yarns. This structure thus constitutes a mechanically actuated electrical switch, sensitive to force or pressure.
Preferably, the types of crossover structures used from patent application WO-01/75778 are those pertaining to woven fabrics that incorporate non-composite conductive yarns; that is monofilament yarns or multifilament yarns comprising a plurality of similar monofilaments, that exhibit a uniformly conductive outer surface. This excludes those composite yarns described in WO-01/5778 that comprise both conductive and insulative elements but includes the majority of commercially available conductive yarns, which tend to be composed of pure metallic conductive filaments or filaments that are uniformly coated with a metallic or non-metallic (usually carbon) conductive material.
The preferred separation technique for use with non-composite conductive yarns in a woven textile is the use of a weave structure with floats, a term applied to a portion of weft yarn that passes over or under more than one warp yarn or vice-versa, as described in WO-01/75778.
The majority of prior art on textile resistive elements is concerned with electrical heating. Much of this prior art, for instance US-2001/0002669, U.S. Pat. No. 6,452,138, GB-A-657,729 and GB-A-428,036, is in turn concerned with the creation of a suitably flexible non-textile heating element which is then incorporated in or appended to a textile substrate. In some cases, for instance U.S. Pat. Nos. 6,172,344, 4,764,665 and 4,149,066, the heating element is formed as an electrically conductive coating or surface upon a textile substrate. These techniques suffer the disadvantages of complex, many-stage production processes and deterioration in use due to the heating element or material becoming separated from its textile substrate.